Migrations are change-control events. The checklist should establish a before state, define the intended redirect and canonical behavior, verify the launch, and monitor for deviations. The risk comes from multiple technical signals changing at once, not from migration as a concept.
Evidence required before launch: a crawlable URL inventory, current canonicals, response codes, important internal links, sitemap membership, and search performance references for priority pages. Keep this baseline unchanged so post-launch differences can be compared directly.
Pass condition for changed URLs: each retired URL that has a clear replacement uses a direct 301 redirect to the most equivalent destination, without unnecessary chains. After launch, verify the new destination, canonical, internal links, and sitemap representation.
Recheck the property within 48 hours so implementation errors are identified while the deployment context is still fresh.
Fail condition: intended permanent replacements do not return 301, intended temporary behavior is confused with 302 handling, old URLs return unexpected 404 responses when an equivalent replacement exists, canonicals point back to retired locations, or internal links continue to route through old paths. Severity is critical when the issue affects major templates or a large share of organic landing pages.
Owner: engineering owns routing and deployment, platform teams may own edge or server rules, content teams may own changed internal links, and SEO owns the migration acceptance criteria and validation record.
Corrective action should restore the intended destination directly rather than stacking additional redirects on top of a broken mapping.
Validation: recrawl the migrated area, compare it with the baseline, confirm response and canonical behavior, update the sitemap to current URLs, and monitor Search Console for unexpected indexing or coverage changes.
Keep the migration log with the release so any later decline can be traced to a documented technical change rather than assumed to be caused by the migration itself.